This invention relates to a vehicle traction control system and, more particularly, to such a system which provides for such control by control of both the brakes of the driven wheels and engine torque output.
It is a common experience with automotive vehicles for excessive wheel slip to occur during vehicle acceleration when the operator initiated engine torque delivered to the vehicle driven wheels are such that the frictional forces between the tire and the road surface are overcome. While a small amount of slip between the tire and road surface is necessary in order to achieve a driving force, excessive slip results in the reduction of effective driving force and in the deterioration in the lateral stability of the vehicle.
Various methods have been proposed for preventing an excessive slip condition of the driven wheels of a vehicle by limiting the slip between the wheel and the road surface at a value that will achieve a maximum transfer of driving force from the driven wheels to the road surface. For example, in one method, the output power of the engine is reduced by reducing the amount of fuel delivered to the engine when an excessive slip condition is detected. In another method, the brakes of the spinning wheel are applied when the excessive slip condition is detected. In yet another known method both wheel brake application and engine output power are controlled to limit acceleration wheel spin.
In those systems in which the wheel brakes are applied to limit acceleration wheel slip, it is desirable to minimize the amount and duration of brake application so as to minimize the amount of energy being absorbed by the brakes. This is accomplished in those systems where both wheel brakes and engine output power are controlled for acceleration slip control by reduction of engine torque output either simultaneously with the application of brakes when an excessive acceleration slip condition is detected or subsequent to the application of the brakes in response to such a condition.